The 27-year-old Himmelberg has been in career-best form in 2023, playing a key role in defence, having previously made his name as a high-marking forward who could also pinch-hit in the ruck.
The Wagga Wagga product joined the Giants Academy as a teenager and the new deal effectively ensures he will end his career as a one-club player.
"We've always been really confident Harry saw his future at the club and his signature is a great endorsement of our program on and off the field," said GWS general manager of football Jason McCartney.
"Harry's been an important part of our club since his days in the academy and has blossomed into a key member of our side.
"His versatility as a player has never been more on show that this season when he's kicked important goals, taken incredible marks and then switched to defence where he's been ultra-consistent.
"He's also continued to grow as a leader and is part of our emerging leaders' group, which is a great reflection of his value to our club."
Under the stewardship of Kingsley, the sixth-placed Giants are riding a best-ever run of seven successive wins heading into Saturday night's derby at home against Sydney.
As a free agent, Himmelberg would have had plenty of suitors in the upcoming trade period had he decided to look elsewhere.
Himmelberg joins first-round draft pick Lachie Ash in the group of key Giants players to have re-signed in recent weeks.
Himmelberg's new contract is understood to be worth more than $800,000 per season.
He has played 145 games to date for GWS and kicked 160 goals.
